involved in a relation or calling is a juristic way of saying that one who deals with another in such a relation or with another who professes such a calling is justified in assuming the skill and diligence ordinarily involved therein, so that the law holds those in the relation or engaged in the calling to that standard in order to maintain the general security. In other words another, though closely related, postulate of civilized society is involved. It is worth a moment's digression to suggest that such things show how little the historical categories of delict and contract represent any essential or inherent need of legal thinking. Austin thought that "the distinction of obligations (or of duties corresponding to rights against persons specifically determined) into obligations which arise from contracts, obligations which arise from injuries, and obligations which arise from incidents which are neither contracts nor injuries," was a "necessary distinction," without which a "system of law evolved in a refined community" could not be conceived. This "necessary" systematic scheme, which must be "a constituent part" of any imaginable developed legal system, is but the Roman division into obligations _ex contractu_, obligations _ex delicto_ and obligations _ex uariis causarum figuris_, in which the third category is obviously a catch-all. In trying to fit our law into this necessary scheme, we find three types of cases must go in the third: (a) Duties or liabilities attached by law to a relation, (b) duties imposed by law to prevent unjust enrichment, (c) duties involved in an office or calling. In the third of these our Anglo-American procedure allows recovery either _ex delicto_ or _ex contractu_. In the second our law sometimes goes on a property theory of constructive trust. In the first duties are sometimes sanctioned affirmatively by conferring legal powers or negatively by legal non-restraint of natural powers, as in the law of domestic relations, where the wife has a power to pledge the husband's credit for necessaries and the law does not interfere with the parent's administering reasonable "correction" to the child. Are we to say that these dogmatic departures of our law from the Roman scheme are inconceivable or that because of them our law is not matured or was not "evolved in a refined community?" Or are we to say that Austin derived his systematic ideas, not from scientific study of English law, but from scientific study of Roman law in a German university? Are we to say that we cannot "imagine coherently" a system of law which enforces warranties indifferently _ex contractu_ or _ex delicto_ as our law does, or which goes further and applies the contract measure of damage _ex delicto_ as does the law of Massachusetts? But enough of this. What we have here is not any necessary distinction. It is rather what Austin calls a "pervading notion," to be found generally in the systematic ideas of developed